(1) Field of the Invention
The present invention relates to a method of producing nuclear magnetic resonance of an object and to an apparatus therefor. Particularly, the invention relates to a method of producing nuclear magnetic resonance in a plurality of slices of an object and to an apparatus therefor.
(2) Description of the Prior Art
The phenomenon of nuclear magnetic resonance has been utilized for the structural analysis of organic compounds and for the study of physical properties in the field of physics, and is currently finding applications in the field of medical diagnosis. In particular, it has been reported that data signals related to T.sub.1 relaxation time (often called spin-lattice relaxation time or longitudinal relaxation time) that serve as nuclear magnetic resonance signals, are very effective for detecting cancer.
An apparatus which is so constructed as to utilize nuclear magnetic resonance signals for medical diagnosis is usually called a nuclear magnetic resonance imaging apparatus or a magnetic resonance imaging apparatus. Nuclear magnetic resonance imaging technology has been disclosed in U.S. Pat. No. 4,458,203 issued to Picker International, Limited, on July 3, 1984, according to which nuclear magnetic resonance signals of one or more slices are obtained within a T.sub.1 relaxation time of a slice of an object. Therefore, the time for measurement can be greatly reduced compared with when nuclear magnetic resonance signals of other slices are obtained after the T.sub.1 relaxation time of a slice has lapsed.
According to this technology, however, a series of selective radio frequency .pi./2 pulses are successively applied to the object after the nonselective radio frequency .pi. pulses are applied to the object. Therefore, homogeneity is lost among the nuclear magnetic resonance signal images of the slices of the object selected by the selective radio frequency .pi./2 pulses. That is, images of individual slices possess different T.sub.1 relaxation time enhance values. This is not desirable from the viewpoint of medical diagnosis.